Phase-change optical recording medium and recording method and apparatus for the same

ABSTRACT

An optical recording medium has a phase-change recording layer containing Sb and Te as essential elements therefor, to which is added at least one element selected from the group consisting of Ag, Au, Cu, Zn, B, Al, Ga, In, Si, Ge, Sn, Pb, N, P, Bi, La, Ce, Gd, and Tb, the recording layer being capable of assuming an amorphous phase changed from a crystalline phase by the application of a laser beam thereto, thereby optically recording information. Recording marks are formed in the recording medium by converting a light emission wave of laser beam into a recording pulse train comprising a plurality of on-pulses and off-pulses, with a recording frequency being continuously changed corresponding to the location of each of the recording marks in the radial direction of said recording medium. A recording apparatus has laser beam driving circuit means, signal generation means, and signal transmission means for achieving the above recording method.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an optical recording mediumcomprising a phase-change recording material which is opticallychangeable by the application thereto of a light beam so as to carry outrecording, reproducing, and overwriting of information, and moreparticularly to a phase-change optical recording medium capable ofrecording information with high density at high recording linearvelocity.

[0003] In addition, the present invention also relates to a recordingmethod and apparatus for the above-mentioned phase-change opticalrecording medium by a Constant Angular Velocity (CAV) system or aConstant Linear Velocity (CLV) system which is achieved by dividing therecording area of the recording medium into a plurality of sections inthe radial direction of the recording medium.

[0004] 2. Discussion of Background

[0005] To reproduce or record information in an optical disc with highdensity by using a laser beam, there is conventionally known theoverwriting mode in which recording marks are formed in the optical discby the application of a plurality of short-length pulse trains asdisclosed in Japanese Laid-Open Patent Application 3-185628. However,the above-mentioned overwriting mode has the drawback that the laserpower becomes partially insufficient. More specifically, in the casewhere the optical disc is rotated at a constant number of revolutions,the relative speed of the laser spot is not constant between a recordingarea at the inner circumference of the disc and that at the outercircumference thereof, viewed in a radial direction of the disc. In sucha case, the laser power becomes insufficient in the area where therelative speed of the laser spot is fast. Furthermore, there will occura new problem that design of the circuit becomes difficult.

[0006] To solve the above-mentioned problems, there is a proposal inJapanese Laid-Open Patent Application 6-12674. This proposal is thatwhen an input signal with a particular wave form, for example, an eightto fourteen modulation signal (EFM signal) is given to an optical disc,the wave form of laser is modulated depending upon the linear velocity.More specifically, the laser is modulated into a short-length train ofpulses when the linear velocity is slower than a predetermined value(L0); and the laser is modulated into one pulse which is made slightlyshorter than the corresponding recording mark when the linear velocityis faster than the aforementioned value (L0).

[0007] There is an increasing demand for development of a phase-changeoptical recording medium and a recording method therefor, which will beable to achieve high-density recording such that the recording capacitythereof is the same or more than that of DVD-ROM, and attain high-speedrecording at a linear velocity of 2 times or more (about 7 m/s or more)that of the nominal speed for the DVD-ROM. However, when such an opticalrecording medium is subjected to the above-mentioned CAV or CLVrecording method, it is conventionally known that good recordingcharacteristics cannot be obtained with respect to jitter value byslightly shortening the input Pulse width. On the contrary, when theaforementioned conventional method, as proposed in Japanese Laid-OpenPatent Application 6-12674, of modulating laser into a short-lengthtrain of pulses at the lower linear velocity side, good results can beproduced. It is considered that, in Japanese Laid-Open PatentApplication 6-12674, the above-mentioned recording method is employedbecause the optical disc employs a composition close to a compound ofGe₂Sb₂Te₅.

[0008] However, when recording is carried out using the modulated laserwith the pulse width being fixed so as not to be deformed at the higherlinear velocity side, the pulse width becomes too short in the recordingarea of the lower linear velocity side, that is, at an innercircumference of the recording medium. In this area, there is a tendencyof impairing the jitter value due to insufficient recording power. It isconsidered that such a phenomenon is also caused by the composition of arecording layer for use in the optical recording medium.

SUMMARY OF THE INVENTION

[0009] Accordingly, it is a first object of the present invention toprovide a phase-change optical recording medium free from theabove-mentioned conventional drawbacks, capable of achievinghigh-density recording such that the recording capacity thereof is thesame or more than that of the DVD-ROM, and attaining high-speedrecording at a recording linear velocity in the range of 3.0 to 20 m/s.

[0010] A second object of the present invention is to provide arecording method for the above-mentioned phase-change optical recordingmedium.

[0011] A third object of the present invention is to provide a recordingapparatus for the above-mentioned phase-change optical recording medium.

[0012] The above-mentioned first object of the present invention can beachieved by an optical recording medium for recording information,comprising a phase-change recording layer comprising Sb and Te asessential elements therefor, to which is added at least one elementselected from the group consisting of Ag, Au, Cu, Zn, B, Al, Ga, In, Si,Ge, Sn, Pb, N, P, Bi, La, Ce, Gd, and Tb, the recording layer beingcapable of assuming an amorphous phase changed from a crystalline phaseby the application of a laser beam thereto, thereby optically recordinginformation.

[0013] In the above-mentioned optical recording medium, the Sb and Te,and at least one element selected from the aforementioned groupconstitute a eutectic phase-change material, with Sb and Te serving asthe main components therefor, and at least one element serving as anadditional component in an atomic percentage of 17% or less in theeutectic phase-change material.

[0014] It is preferable that there is a difference in reflectance of 30%or more between (a) the crystalline phase and (b) the amorphous phaseformed by the application of the laser beam to the crystalline phase ata recording linear velocity ranging from 3 to 20 m/s.

[0015] The second object of the present invention can be achieved by amethod for optically recording information, using an optical recordingmedium comprising a phase-change recording layer comprising Sb and Te asessential elements therefor, to which is added at least one elementselected from the group consisting of Ag, Au, Cu, Zn, B, Al, Ga, In, Si,Ge, Sn, Pb, N, P, Bi, La, Ce, Gd, and Tb, the recording layer beingcapable of assuming an amorphous phase changed from a crystalline phaseby the application of a laser beam thereto, thereby optically recordinginformation by forming recording marks therein, wherein when therecording marks are formed in the optical recording medium, a lightemission wave of the laser beam is converted into a recording pulsetrain comprising a plurality of on-pulses and each off-pulse subsequentto the on-pulses, with a recording frequency v (v=1/Tw where Tw is awindow width) being continuously changed corresponding to the locationof each of the recording marks in the radial direction of the recordingmedium, either in the direction from an inner circumference towards anouter circumference of the recording medium, or in the direction fromthe outer circumference towards the inner circumference of the recordingmedium.

[0016] The third object of the present invention can be achieved by arecording apparatus for recording information comprising laser beamdriving circuit means for carrying out a recording method for opticallyrecording information, using an optical recording medium comprising aphase-change recording layer comprising Sb and Te as essential elementstherefor, to which is added at least one element selected from the groupconsisting of Ag, Au, Cu, Zn, B, Al, Ga, In, Si, Ge, Sn, Pb, N, P, Bi,La, Ce, Gd, and Tb, the recording layer being capable of assuming anamorphous phase changed from a crystalline phase by the application of alaser beam thereto, thereby optically recording information by formingrecording marks therein, wherein when the recording marks are formed inthe optical recording medium, a light emission wave of the laser beam isconverted into a recording pulse train comprising a plurality ofon-pulses and each oft-pulse subsequent to the on-pulses, with arecording frequency v (v=1/Tw where Tw is a window width) beingcontinuously changed corresponding to the location of each of therecording marks in the radial direction of the recording medium, eitherin the direction from an inner circumference towards an outercircumference of the recording medium, or in the direction from theouter circumference towards the inner circumference of the recordingmedium, a plurality of on-pulses having a pulse width comprising (1) apulse width portion fixed with an identical time constant (T), and (2) apulse width portion determined by multiplying the window width (Tw) by aconstant, signal generation means for generating a signal correspondingto the time constant, and signal transmission means for transmitting thesignal to the driving circuit means.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] A more complete appreciation of the invention and many of theattendant advantages thereof will be readily obtained as the samebecomes better understood by reference to the following detaileddescription when considered in connection with the accompanyingdrawings, wherein:

[0018]FIG. 1 is a cross-sectional view which shows the structure of aphase-change optical recording medium according to the presentinvention.

[0019]FIG. 2 is a chart in explanation of the recording method accordingto the present invention.

[0020]FIG. 3 is a chart which shows the relationship between therecording linear velocity and the on-pulse width.

[0021]FIG. 4 is a chart which shows the relationship between therecording linear velocity in the recording method employed in Example 2and the pulse duty ratio thereof.

[0022]FIG. 5 is a chart which shows the jitter performance in therecording methods employed in Examples 1 and 2.

[0023]FIG. 6 is a chart which shows the relationship between therecording linear velocity in the recording method employed in Example 3and the on-pulse duty ratio.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] The optical recording medium of the present invention ischaracterized in that the recording layer comprises Sb and Te asessential elements therefor, to which is added at least one elementselected from the group consisting of Ag, Au, Cu, Zn, B, Al, Ga, In, Si,Ge, Sn, Pb, N, P, Bi, La, Ce, Gd, and Tb, with the above-mentionedessential elements of Sb and Te, and at least one element selected fromthe above-mentioned group constituting a eutectic phase-change material.It is preferable that at least one element selected to serve as anadditional component being contained in an atomic percentage of 17% orless in the eutectic phase-change material. As mentioned above, therecording layer for use in the present invention is different from theconventional one comprising a compound substantially the same asGe₂Sb₂Te₅.

[0025]FIG. 1 is a cross-sectional view which shows the structure of aphase-change optical recording medium according to the presentinvention. In an optical recording medium shown in FIG. 1, a firstdielectric layer 2 (serving as a lower protective layer), a recordinglayer 3, a second dielectric layer 4 (serving as an upper protectivelayer), and a metal reflection layer 5 (serving as a light reflectionand heat dissipation layer) are successively formed on a substrate 1which bears thereon a guide groove. Further, a protective layer 6comprising an UV curing resin may be preferably overlaid on the metalreflection layer 5.

[0026] In particular, it is preferable that the recording layer 3comprise a composition of AgInSbTe.

[0027] It is desirable that the first or second dielectric layer 2 or 4comprise a composition of ZnS—SiO₂.

[0028] It is also desirable that the metal reflection layer 5 comprise acomposition of Al—Ti.

[0029] As the material for the substrate 1, there can be generallyemployed glass, ceramic materials, and resins. A resin substrate is mostpreferable in light of the molding characteristics. Representativeexamples of the resin for the substrate are polycarbonate resin, acrylicresin, epoxy resin, polystyrene resin, polyethylene resin, polypropyleneresin, silicone resin, fluororesin, ABS resin, and urethane resin. Ofthese resins, the polycarbonate resin is preferably employed because ofthe advantages over other resins in terms of processability and opticalproperties. The substrate may be prepared in the form of a disc, card,or sheet.

[0030] Exemplary film-forming conditions of each layer in a film-formingchamber are shown below

[0031] [First dielectric layer (ZnS—SiO₂ layer)]

[0032] applied electric power: 3 kW

[0033] argon (Ar) gas pressure: 2 mmTorr (atmospheric pressure in afilm-forming chamber)

[0034] [Recording layer (AgInSbTe layer)]

[0035] applied electric power: 1 kW

[0036] argon (Ar) gas pressure; 2 mmTorr (atmospheric pressure in afilm-forming chamber)

[0037] [Second dielectric layer (ZnS—SiO₂ layer)]

[0038] applied electric power: 3 kW

[0039] argon (Ar) gas pressure: 2 mmTorr (atmospheric pressure in afilm-forming chamber)

[0040] [Metal reflection layer (Al layer)]

[0041] applied electric power: 9 kW

[0042] argon (Ar) gas pressure: 3 mmTorr (atmospheric pressure in afilm-forming chamber)

[0043] When the recording layer comprises a composition of AgInSbTe, thepresence of the element Ag can effectively improve the recordingcharacteristics and the preservation stability. However, the increase inan amount of Ag lowers the crystalline phase transition speed of therecording layer, so that it becomes difficult to cope with highrecording linear velocity. To cope with the rise of recording linearvelocity, the content of Sb or In may be increased. However, when thecontent of Sb is increased to cope with high recording linear velocity,there is a risk that the overwriting characteristics and thepreservation reliability under the circumstances of high temperature andhigh humidity will suddenly drop. When the content of In is increased,it is preferable that the atomic percentage of the element of In be 0.1or less.

[0044] The first dielectric layer and the second dielectric layer areformed by a variety of vapor growth methods, for example, vacuumdeposition, sputtering, and electron beam evaporation. The thickness ofthe first or second dielectric layer varies depending on the function ofthe layer as a heat-resistant layer or multiple-interference layer. Itis preferable that the first dielectric layer have a thickness of 50 to110 nm, or 170 to 215 nm. When the thickness of the first dielectriclayer is less than 50 nm, the first dielectric layer cannot work toprotect the substrate from the influence caused by heat accumulation inthe recording layer. When the thickness of the first dielectric layer ismore than 215 nm, the peeling of the first dielectric layer from theinterface can be prevented. It is also preferable that the thickness ofthe second dielectric layer be in the range of 10 to 30 nm. The seconddielectric layer with such a thickness, the decrease of recordingsensitivity and the excessive heat accumulation can be prevented.

[0045] To erase the recorded information without fail in the course ofoverwriting operation, the conventional recording material needsdelicate control of temperature so that the recording layer is heated ataround the crystallization temperature thereof. In contrast to this, theerasing characteristics of the optical recording medium of the presentinvention are excellent. Further, consideration may be just given torapid cooling after the recording layer is irradiated with a laser beamin the course of recording. Therefore, a stable recording mark can beformed in the optical recording medium of the present invention by boththe CAV and CLV recording methods.

[0046] According to the present invention, recording marks are formed inthe above-mentioned optical recording medium by converting a lightemission wave of the laser beam into a recording pulse train comprisinga plurality of on-pulses and each off-pulse subsequent to the on-pulses,with a recording frequency v (v=1/Tw where Tw is a window width) beingcontinuously changed corresponding to the location of each of therecording marks in the radial direction of the recording medium, eitherin the direction from an inner circumference towards an outercircumference of the recording medium, or in the direction from theouter circumference towards the inner circumference of the recordingmedium.

[0047] In the aforementioned recording method, there may be a differencein reflectance of 30% or more between (a) the crystalline phase and theamorphous phase formed by the application of the laser beam to thecrystalline phase at a recording linear velocity ranging from 3 to 20m/s.

[0048]FIG. 2 is a chart in explanation of one embodiment of theabove-mentioned recording method. In this case, the recording marks areformed in the recording medium in such a manner that a plurality ofon-pulses has a pulse width comprising a pulse width portion (dTmp)fixed with an identical time constant (T), and a pulse width portion(Tmp) determined by multiplying the window width (Tw) by a constant.

[0049] When the above-mentioned recording method as shown in FIG. 2, thepulse width of the on-pulses varies depending upon the recording linearvelocity, as indicated by a graph 1 shown in FIG. 3,. In comparison withthe pulse width obtained by the above-mentioned recording methodaccording to the present invention, the pulse width obtained by theconventional recording method consists of only the pulse width portion(Tmp), so that the pulse width is constant regardless of the recordinglinear velocity, as indicated by a graph 2 in FIG. 3.

[0050] As is apparent from the graph 1 shown in FIG. 3, theabove-mentioned recording method of the present invention can increasethe pulse width at the lower linear velocity side, in other words, atthe inner circumference of the recording medium. The result is that astable recording mark can be formed in the recording medium by any ofthe CAV or CLV recording system. Namely, it is possible to prevent thedeterioration of jitter performance which is conventionally caused insuch a way that the recording power becomes insufficient due to thenarrow pulse width at the inner circumference of the recording medium.

[0051] With respect to the pulse width portion (Tmp) in FIG. 2, it ispreferable that the ratio of the constant to the window width (Tw) is0.5 or less. When the aforementioned ratio is 0.5 or less, a stablepulse train for driving laser diode (LD) can be obtained. To be morespecific, the off-pulses become shorter as the recording linear velocitybecomes higher, in other words, as the window width becomes narrower. Insuch a case, a pulse decay time constant for laser diode (LD) cannot besecured, so that it becomes difficult to perform stable irradiation ofthe recording medium with the laser beam.

[0052] Furthermore, with respect to the pulse width portion (dTmp) fixedwith an identical time constant (T), it is preferable that the ratio ofthe time constant (T) to Tw be 0.8 or less in a maximum recordingfrequency used, and 0.2 or more in a minimum recording frequency used.When such threshold values are provided, the pulse width can beinhibited from becoming extremely narrow at the lower linear velocityside, so that deterioration of jitter performance due to insufficientrecording power can be effectively prevented.

[0053] In the case of the graph 1 in FIG. 3, both thresholds values aresatisfied. As a result, the duty ratio becomes larger at the lowerlinear velocity side, and therefore the jitter performance becomesbetter in the recording method indicated by the graph 1 than in theconventional recording method indicated by the graph 2. In FIG. 3, thisis expressed by the pulse width instead of the duty ratio forconvenience.

[0054] The recording method according to the present invention mayemploy in combination a recording mode (a) in which a plurality ofon-pulses has a pulse width comprising a pulse width portion (dTmp)fixed with an identical time constant (T), and a pulse width portion(Tmp) determined by multiplying the window width (Tw) by a constant, anda recording mode (b) in which a plurality of on-pulses has such a pulsewidth that is adjusted to have a constant duty ratio to the window width(Tw) in such a manner that the recording mode (a) and the recording mode(b) are switched at an intermediate recording frequency between amaximum recording frequency and a minimum recording frequency.

[0055] A graph 1 in FIG. 4 shows the relationship between the duty ratioto the pulse width (Tw) at each linear velocity when the above-mentionedrecording method using the recording mode (a) and the recording mode (b)in combination is carried out.

[0056] When compared with the graph 1, according to a graph 2 of theconventional recording method, an off-pulse portion becomes shorter asthe window width decreases at the higher linear velocity. Therefore, apulse decay time constant of LD cannot be secured, so that stableirradiation of the recording medium with the laser beam cannot beachieved. At the lower linear velocity side, the pulse width becomes toonarrow to obtain sufficient recording power, so that the jitterperformance is lowered.

[0057] It is preferable that the recording mode (a) be carried out in arange between the intermediate recording frequency and the minimumrecording frequency. This case is indicated by a graph 1 in FIG. 6. Itis possible to prevent the deterioration of jitter values due toinsufficient recording power when the pulse width becomes too narrowerat the lower linear velocity side. A graph 2 in FIG. 6 shows therelationship between the linear velocity and the duty ratio when theconventional recording method is employed.

[0058] To effectively prevent the above-mentioned drawbacks, it ispreferable that the constant duty ratio in the recording mode (b) be 0.8or less.

[0059] To achieve the aforementioned recording methods, a recordingapparatus of the present invention comprises laser beam driving circuitmeans, signal generation means for generating a signal corresponding tothe aforementioned time constant, and signal transmission means fortransmitting the signal to the driving circuit means. Owing to such arecording apparatus, the pulse application time constant can be smoothlychanged. It is said that the recording apparatus particularly suitablefor CAV recording can be obtained.

[0060] Other features of this invention will become apparent in thecourse of the following description of exemplary embodiments, which aregiven for illustration of the invention and are not intended to belimiting thereof.

EXAMPLE 1

[0061] [Fabrication of phase-change optical recording medium]

[0062] On a polycarbonate substrate, a first dielectric layer(ZnS—SiO₂), a recording layer (AgInSbTe), a second dielectric layer(ZnS—SiO₂), and a metal reflection layer (Al—Ti) were successivelyoverlaid by the sputtering method. An UV-curing resin was coated on themetal reflection layer by spin coating to provide a protective layerthereon.

[0063] Each of the above-mentioned layers was formed under the followingfilm-forming conditions:

[0064] [First dielectric layer (ZnS—SiO₂ layer)]

[0065] applied electric power: 3 kW

[0066] argon (Ar) gas pressure: 2 mmTorr (atmospheric pressure in afilm-forming chamber)

[0067] [Recording layer (AgInSbTe layer)]

[0068] applied electric power: 1 kW

[0069] argon (Ar) gas pressure: 2 mmTorr (atmospheric pressure in afilm-forming chamber)

[0070] [Second dielectric layer (ZnS—SiO₂ layer)]

[0071] applied electric power; 3 kW

[0072] argon (Ar) gas pressure: 2 mmTorr (atmospheric pressure in afilm-forming chamber)

[0073] [Metal reflection layer (Al—Ti layer)]

[0074] applied electric power: 9 kW

[0075] argon (Ar) gas pressure: 2 mmTorr (atmospheric pressure in afilm-forming chamber)

[0076] Thus, a phase-change optical recording medium No. 1 according tothe Present invention was fabricated.

[0077] Using the optical recording medium No. 1, the CAV recording wascarried out in such a manner that the recording linear velocities wereset to 3.49 m/sec at the innermost circumference and 8.5 m/sec at theoutermost circumference. In this case, a plurality of on-pulses wascontrolled so that a pulse width was composed of a pulse width portionfixed with a time constant of 8 nsec, and a pulse width portiondetermined by multiplying the window width (Tw) by a constant of ⅙, asshown in FIG. 2. A portion (dTera) shown in FIG. 2 was set bymultiplying the window width (Tw) by a constant of ⅙. In this case, thewindow width was multiplied by a positive constant, that is, +⅙. It wasalso possible to multiply the window width by a negative constant, thatis, −⅙. Further, the constant represented by 1/n where n is an integeris favorable in light of the circuit.

[0078] The results of the recording operation are shown in FIG. 5. As isapparent from the graph in FIG. 5, the jitter value can be reduced atthe lower linear velocity side, thereby achieving stable recording.

[0079] For comparison, when recording was carried out by merely fixingthe time constant, as shown in FIG. 5, the jitter value increased as awhole, in particular, at the lower linear velocity side.

EXAMPLE 2

[0080] Using the same phase-change optical recording medium No. 1fabricated in Example 1, the recording was carried out by combining thepreviously mentioned recording mode (a) and recording mode (b). To bemore specific, the recording mode (a) was carried out in such a mannerthat the pulse width of a plurality of on-pulses was composed of a pulsewidth portion fixed with a time constant of 11.5 nsec, and a pulse widthportion determined by multiplying the window width (Tw) by a constant of⅙, as shown in FIG. 2. The recording mode (a) was adapted from theinnermost circumference of the recording medium up to a recordingposition of which the window width was 1.7 times that at the innermostcircumference. In other words, the recording mode (a) was switched tothe recording mode (b) at the position around half the distance of aradius of the recording medium. At this position, the recording linearvelocity was about 6 m/sec.

[0081] Outward from this position, the recording mode (b) was carriedout with the pulse width of a plurality of on-pulses being adjusted tohave a constant duty ratio to the window width of 0.6.

[0082] In this case, the duty ratio varied depending upon the recordinglinear velocity as indicated by a graph 1 shown in FIG. 4. In contrastto the graph 1, a graph 2 shows the relationship between the duty ratioand the recording linear velocity when the recording mode (a) employedin Example 2 was adapted up to the outermost circumference. In thiscase, as indicated by the graph 2, the duty ratio exceeded 0.8 at theposition of which the window width was 2.2 times that of the innermostcircumference, and the recording was impossible outerward therefrom.

[0083] The results of the recording operation are shown in FIG. 5 interms of the jitter value depending upon the recording linear velocity.

EXAMPLE 3

[0084] Using the same phase-change optical recording medium No. 1fabricated in Example 1, the recording was carried out by combining thepreviously mentioned recording mode (a) and recording mode (b). To bemore specific, the recording mode (b) was first carried out with thepulse width of a plurality of on-pulses being adjusted to have aconstant duty ratio to the window width of 0.5.

[0085] The recording mode (b) was adapted from the innermostcircumference of the recording medium up to a position of which thewindow width was 1.7 times that of the innermost circumference of therecording medium. In other words, the recording mode (b) was switched tothe recording mode (a) at the position around half the distance of aradius of the recording medium. At this position, the recording linearvelocity was about 6 m/sec.

[0086] Outerward from this position, the recording mode (a) was carriedout in such a manner that the pulse width of a plurality of on-pulseswas composed of a pulse width portion fixed with a time constant of 8nsec, and a pulse width portion determined by multiplying the windowwidth (Tw) by a constant of ⅙.

[0087] As a result, the jitter value was almost the same as thatobtained in Example 2.

[0088] Japanese Patent Application No. 11-131926 filed May 12, 1999 ishereby incorporated by reference.

What is claimed is:
 1. An optical recording medium for recordinginformation, comprising a phase-change recording layer comprising Sb andTe as essential elements therefor, to which is added at least oneelement selected from the group consisting of Ag, Au, Cu, Zn, B, Al, Ga,In, Si, Ge, Sn, Pb, N, P, Bi, La, Ce, Gd, and Tb, said recording layerbeing capable of assuming an amorphous phase changed from a crystallinephase by the application of a laser beam thereto, thereby opticallyrecording information.
 2. The optical recording medium as claimed inclaim 1, wherein (1) said Sb and Te, and (2) said at least one elementselected from the group consisting of Ag, Au, Cu, Zn, B, Al, Ga, In, Si,Ge, Sn, Pb, N, P, Bi, La, Ce, Gd, and Tb, constitute a eutecticphase-change material, with said Sb and Te serving as the maincomponents therefor, and said at least one element serving an additionalcomponent in an atomic percentage of 17% or less in said eutecticphase-change material.
 3. The optical recording medium as claimed inclaim 1, wherein there is a difference in reflectance of 30% or morebetween (a) said crystalline phase and (b) said amorphous phase formedby the application of said laser beam to said crystalline phase at arecording linear velocity ranging from 3 to 20 m/s.
 4. A method foroptically recording information, using an optical recording mediumcomprising a phase-change recording layer comprising Sb and Te asessential elements therefor, to which is added at least one elementselected from the group consisting of Ag, Au, Cu, Zn, B, Al, Ga, In, Si,Ge, Sn, Pb, N, P, Bi, La, Ce, Gd, and Tb, said recording layer beingcapable of assuming an amorphous phase changed from a crystalline phaseby the application of a laser beam thereto, thereby optically recordinginformation by forming recording marks therein, wherein when saidrecording marks are formed in said optical recording medium, a lightemission wave of said laser beam is converted into a recording pulsetrain comprising a plurality of on-pulses and each off-pulse subsequentto said on-pulses, with a recording frequency v (v=1/Tw where Tw is awindow width) being continuously changed corresponding to the locationof each of said recording marks in the radial direction of saidrecording medium, either in the direction from an inner circumferencetowards an outer circumference of said recording medium, or in thedirection from the outer circumference towards the inner circumferenceof said recording medium.
 5. The recording method as claimed in claim 4,wherein there is a difference in reflectance of 30% or more between (a)said crystalline phase and said amorphous phase formed by theapplication of said laser beam to said crystalline phase at a recordinglinear velocity ranging from 3 to 20 m/s.
 6. The recording method asclaimed in claim 4, wherein said plurality of on-pulses has a pulsewidth comprising (1) a pulse width portion fixed with an identical timeconstant (T), and (2) a pulse width portion determined by multiplyingsaid window width (Tw) by a constant.
 7. The recording method as claimedin claim 6, wherein in said pulse width portion fixed with an identicaltime constant (T), the ratio of said time constant (T) to Tw is 0.8 orless in a maximum recording frequency used, and 0.2 or more in a minimumrecording frequency used.
 8. The recording method as claimed in claim 6,wherein in said pulse width portion determined by multiplying saidwindow width (Tw) by a constant, the ratio of said constant to saidwindow width is 0.5 or less.
 9. The recording method as claimed in claim4, using in combination: (a) a recording mode in which said plurality ofon-pulses has a pulse width comprising (1) a pulse width portion fixedwith an identical time constant (T), and (2) a pulse width portiondetermined by multiplying said window width (Tw) by a constant, and (b)a recording mode in which said plurality of on-pulses has such a pulsewidth that is adjusted to have a constant duty ratio to said windowwidth (Tw), in such a manner that said recording mode (a) and saidrecording mode (b) are switched at an intermediate recording frequencybetween a maximum recording frequency and a minimum recording frequency.10. The recording method as claimed in claim 9, wherein said recordingmode (a) is carried out in a range between said intermediate recordingfrequency and said minimum recording frequency.
 11. The recording methodas claimed in claim 9, wherein said constant duty ratio in saidrecording mode (b) is 0.8 or less.
 12. A recording apparatus forrecording information comprising: laser beam driving circuit means forcarrying out a recording method for optically recording information,using an optical recording medium comprising a phase-change recordinglayer comprising Sb and Te as essential elements therefor, to which isadded at least one element selected from the group consisting of Ag, Au,Cu, Zn, B, Al, Ga, In, Si, Ge, Sn, Pb, N, P, Bi, La, Ce, Gd, and Tb,said recording layer being capable of assuming an amorphous phasechanged from a crystalline phase by the application of a laser beamthereto, thereby optically recording information by forming recordingmarks therein, wherein when said recording marks are formed in saidoptical recording medium, a light emission wave of said laser beam isconverted into a recording pulse train comprising a plurality ofon-pulses and each off-pulse subsequent to said on-pulses, with arecording frequency V (v=1/Tw where Tw is a window width) beingcontinuously changed corresponding to the location of each of saidrecording marks in the radial direction of said recording medium, eitherin the direction from an inner circumference towards an outercircumference of said recording medium, or in the direction from theouter circumference towards the inner circumference of said recordingmedium, said plurality of on-pulses having a pulse width comprising (1)a pulse width portion fixed with an identical time constant (T), and (2)a pulse width portion determined by multiplying said window width (Tw)by a constant, signal generation means for generating a signalcorresponding to said time constant, and signal transmission means fortransmitting said signal to said driving circuit means.
 13. Therecording apparatus as claimed in claim 12, wherein (a) a recording modein which said plurality of on-pulses has a pulse width comprising (1) apulse width portion fixed with an identical time constant (T), and (2) apulse width portion determined by multiplying said window width (Tw) bya constant, and (b) a recording mode in which said plurality ofon-pulses has such a pulse width that is adjusted to have a constantduty ratio to said window width (Tw), are used in such a manner thatsaid recording mode (a) and said recording mode (b) are switched at anintermediate recording frequency between a maximum recording frequencyand a minimum recording frequency.